Horner Syndrome

Diagnosis

To diagnose Horner syndrome, your doctor will perform a thorough medical examination and specific tests to determine the cause of your symptoms and the location of the nerve damage. The process often involves both clinical evaluation and imaging studies.

Tests to confirm Horner syndrome

Diagnosis may begin with your medical history and an assessment of visible symptoms. An ophthalmologist may confirm the diagnosis using special eye drops. These medicated drops either dilate or constrict the pupils. By comparing the reactions between both eyes, the doctor can identify whether nerve damage is responsible for the abnormal response in the affected eye.

Tests to identify the site of nerve damage

The pattern and severity of symptoms can help determine where along the nerve pathway the problem exists. Additional diagnostic steps may include specialized eye drops to assess nerve function. For instance, if Horner syndrome results from a third-order neuron issue — typically involving the neck or above — the affected eye will show limited dilation compared to the healthy eye.

Your doctor may also order imaging tests to locate the site of the irregularity, such as:

• Magnetic resonance imaging (MRI) to capture detailed images of tissues and structures

• Magnetic resonance angiography (MRA) to evaluate blood vessels

• Computerized tomography (CT) scan for detailed internal images

• Chest X-ray to assess possible nerve compression or abnormalities in the chest

• Carotid ultrasound to evaluate blood flow in the carotid arteries

Treatment

There is no specific treatment for Horner syndrome itself. Instead, management focuses on identifying and treating the underlying cause. Once the root condition is effectively addressed — such as a nerve injury, tumor, or vascular issue — Horner syndrome symptoms may resolve on their own.

Preparing for your appointment

In nonemergency situations, you may first visit a family doctor or ophthalmologist. Depending on your case, you might be referred to a neurologist or neuro-ophthalmologist for further evaluation.

To make the most of your appointment, it’s helpful to prepare in advance.

Before your visit, prepare a list that includes:

• Your symptoms and any changes that have occurred

• Key personal health details, such as past or recent illnesses and injuries

• All medications, vitamins, or supplements you currently take, along with dosages

• Questions you want to ask your doctor

If possible, bring a family member or friend to help remember the information discussed. You can also bring photos of yourself taken before the symptoms started, as they can help your doctor assess eye changes.

Questions to ask your doctor

• What could be causing my symptoms?

• Are there other possible explanations for my condition?

• What tests do I need?

• Is this condition likely temporary or chronic?

• What treatment options are recommended?

• Will I need follow-up tests or evaluations?

What to expect from your doctor

Your doctor will review your medical history, examine your eyes and face, and ask detailed questions, such as:

• When did the symptoms begin?

• Have your symptoms changed or worsened?

• Do you have a history of cancer or neurological conditions?

• Have you experienced any recent injury or trauma?

• Do you have pain in your head, neck, shoulder, or arm?

• Have you had migraines or cluster headaches?

A thorough discussion and diagnostic process help identify the cause of Horner syndrome and guide effective management of the underlying condition.